TRANSEAUBOGS OF THE HURON RIVER VALLEY 423 



principal seat of root activity. The small, fibrous roots of cassandra, 

 andromeda," and the cranberry penetrate it in all directions, and it is 

 from the water which is held among this moss and debris that they 

 derive their water and mineral salts. 



The substratum beneath the tamaracks is also covered by a loose 

 litter of leaves and twigs, with more or less moss. Depending upon 

 the height above the ground water level, this surface layer is of greater 

 or less thickness. In it occur the wide- spreading roots of the tama- 

 rack. During summer and autumn it furnishes admirable conditions 

 for the growth of fungi, and it is penetrated everywhere by their 

 mycelia. 



When bog land is cleared, the decomposition of the surface layers 

 is very rapid, owing to exposure to sunlight and higher temperatures. 

 If the water-table is maintained near the surface, sedges and willows 

 develop as the covering. The annual increment of plant material 

 is often decreased, and in place of the fibrous and porous substratum 

 there is produced a black, close-textured, and plastic muck. 



If ditching and draining are added to clearing, the summer drought 

 dries the surface layer so thoroughly that it often becomes the habitat 

 for many dry-ground weeds. Decay progresses in moist weather 

 under the influences of the higher temperatures resulting from 

 increased absorption of the sun's energy by the dark colored soil. 



4. Mechanical properties. Bog soils in general do not afford as 

 good a foothold for the development of tree species as do the mineral 

 soils. On account of the high water-table, the roots of the plants 

 are not able to penetrate to a depth of more than a few inches. The 

 roots of the tamaracks spread out in all directions from a flat trunk 

 base, and upon the size and strength of these horizontal roots depends 

 the tree's ability to withstand mechanical strains tending to displace 

 it. There can be no doubt but that, in the thick groves in which the 

 tamarack occurs, the interweaving of the roots from adjacent trees 

 becomes of mutual advantage, in so far as the roots function as hold- 

 fast organs. 



5. Diffusion properties. A most important soil property relates 

 to the diffusion of mineral salts. This becomes of especial signifi- 

 cance in saturated stagnant substrata. The mineral salts must be 

 distributed to ' the roots mainly by diffusion, for lateral drainage 



